There is a need for low cost, high performance gyroscopes for navigation systems, precision point systems, and guidance systems. The resonator fiber optic gyroscope (RFOG) is being developed as a new technology using optical fibers, including hollow core fibers) to form a sensing loop. To improve the sensitivity of the gyroscope, longer fiber length may be used to reduce the resonance linewidth, which increases the cavity round trip loss. Polarization and spatial mode filters may also be added to the resonator to prevent unwanted polarization and high order spatial modes from causing bias instability in rotation rate measurements. In addition, it is desirable to output as much optical power as possible to detectors to reduce the shot noise. This requires a large portion of the light being coupled out of the resonator (i.e., high coupling losses for the resonator). All these factors add extra losses to the resonator, making it difficult to achieve the desired gyro performance due to reduced resonator finesse, or significantly increasing the cost for adopting ultra-low-loss components. Component aging is another factor that can affect the cavity round trip loss over time, causing gradual degradation of performance. So it is desirable to find a way for precisely controlling the resonator round trip loss while coupling high power to detectors.